You may look up the quranic ayat in your mushaf (edition
of the Qurân)
This overview was written by the student of islam and is meant to give first
the fundamental meaning of some quranic concepts ( kalimah
) and then something of their richness of meaning and variety.
This abstract is not complete and is not meant to be. Cited verses which
highlight some definitions are not the only verses with the respective
word and the ranking of these words ( kalimah
) does not give them any priority over others.

1.) Root slH: original meaning: to be right, good, honest, uprightas-sâlihûn: the righteous, who do good, free from blemish, upright.
Also related: sulh, peace, reconciliation
as-sâlihât, good works
aslaha (iv): to make whole and sound, to amend, to make a reconciliation or peace.

In the Quran the concept of sâlih is very much tied to iman (îmân - faith):
One of its most frequent phrases is { alladhîna âmanû wa `amilû sâlihât:
those who have faith and do good, righteous works -
those are the rightful owners of the Garden; therein they will abide. }
sura al baqara 2-82 and other verses.

So its is clear that 'good works' sâlihât and 'faith' îmân go hand in hand, the one is strengthened by the other. ( On belief and good deeds, see link )

2. ) Some quranic explanations
'Good works' sâlihât are those done only for the Divine Presence or the Countenance of Allah li-wajhi-LLahi.As described in the Convenant with the people of old (2-83) it includes:

a.) To worship none save Allah,
b.) to be good to parents and, to near kinsmen and to the orphans,
c.) to speak kindly (hasan - good) to everyone,
d.) to perform the daily prayers,
e.) to give the poor-due (zakât - alms)

3.) What may at first seem remarcable is that the Prophets, may Allah grant them peace, did not pray to be 'made righteous' or somehow be 'transformed' spiritually, but they all prayed to be among the righteous as-sâlihûn. So did Sulaimân 27-19, or Yusuf 12-101, may Allah grant them peace, and therefore Muhammad, the Messenger of Allah . So success for us as believers lies in being brought together 5-84 with the righteous ones as-sâlihûn, in a time, when the evil of people is abundant. See hadith

Then Allah takes care of the righteous 7-196, as He does with all of His Prophets (may Allah grant them peace), his masters of the community and his believing servants, when He choses them and places them among the righteous ones. The consequence of belief and right action is to be together with the righteous, who are the best of mankind, especially with Prophet Muhammad .
See for example 29-9.

4.) Many quranic concepts highlight the best of charactertraits, as those of the Prophets, may Allah grant them peace, and His awliyâ [faithful servants].
So - for example - every righteous one sâlih is also truthful sidqun, see 4-69

5.) The quranic verses:

{ And remember the time when WE took a covenant from the Children of Israel-
'You shall worship none but ALLAH and be kind to parents and to the
kindred and orphans and the poor and speak to men kindly and observe
prayer, and pay the Zakât.'
then you turned away in aversion, except a few
of you.} sura al baqara (2) verse 83

{ And whoever obeys Allah and the Apostle, they are with
those upon whom Allah has bestowed favors from among the
prophets and the truthful and the martyrs and the righteous, and a
goodly company are they! } sura an-nisâ (4) verse 69.

And what (reason) have we that we should not believe in
Allah and in the truth that has come to us, while we earnestly
desire that our Lord should cause us to enter with the good
people? sura The Table Spread (5) verse 84.

Surely my guardian is Allah, Who revealed the Book,
and He befriends the good/ righteous. sura The Heights (7) verse 196.

My Lord! Thou hast given me of the kingdom and taught
me of the interpretation of sayings:
Originator of the
heavens and the earth! Thou art my guardian in this world
and the hereafter; make me die a muslim and join me with the
good / righteous. sura Yusuf (12) verse 101.

So he smiled, wondering at her word, and said:
My Lord! grant me that I should be grateful for Thy favor which Thou hast bestowed on me and on my parents, and that I should do good such as Thou art pleased with, and make me enter, by Thy mercy, into Thy servants, the good ones. sura The Spider (27) verse 19.

And (as for) those who believe and do good, We will most surely cause them to enter among the good / righteous. sura The Story (29) verse 9.

And spend out of what We have given you before death comes to one of you, so that he should say:
My Lord! why didst Thou not reprieve me for a little while, so that I should
have given alms and been of the doers of good deeds? sura The Hypocrites (63) verse 10.

The Prophet Muhammad warned his community of the evil of people's souls, especially unbelievers:

It is narrated from Zainab bint Jahsh, that one day the Messenger of Allah entered upon her in a state of fear and
said,
"None has the right to be worshipped but Allah!
Woe to the Arabs from the Great evil that has approached (them).
Today a hole has been opened in the dam of Gog and Magog like this."
The Prophet made a circle with his index finger and thumb.
Zainab bint Jahsh added:
I said, "O Messenger ofAllah's! Shall we be destroyed though there will be righteous people as-sâlihûn among us?"
The Prophet said , "Yes, if the (number) of evil (persons) al-khabathu increases." Bukhari, bk 88 no. 249

[9.] The Wrong-doers

1.) Root zlm: original meaning: putting in a wrong placeaz-zâlimûn: the wrong-doers, evil-doers, those who transgress the proper limit (as in sura al baqara 2-229) and encroach upon the right of some other people.

2. ) Some quranic definitions
The wrong-doers are:
a.) Those who transgress Allah's limits (2-229)
b.) Those who invent a lie and attribute it to Allah (3-94)
c.) Those who are disbelievers (2-254)
d.) Those who take the disbelievers for friends (9-23)
e.) Those who judge by other than the law (sharî`ah) of Allah (5-45)
3.) Those who wrong themselves, their own souls (2-231)

In order to avoid this, i.e. to transgress the limits of Allah, and to be able to do what is expressedly stated in the shariyah, the Muslim has to lie in wait ( al mirsâd ) for his or her selfishness, never giving it free reign, so that it does not pull him off the right path. RT-663uAs the Prophet Muhammad said when he came back from one of his campaigns: You have come forth in the
best way of coming forth: you have come from the smaller
jihad to the geater jihad.' They said: 'And what is the greater
jihad?' He replied: 'The striving [mujahadat]* of God's
servants against their idle desires.
(*also: spiritual warfare).
Suyuti said that al-Khatib [al-Baghdadi] relates it in his 'History' on the authority of Jabir

[10.] The Disbelievers

1.) Rootmeaning

Root kfr: original meaning: to cover up, just as a farmer covers the seeds in the earth, also being ungratefulal-kâfirûn: the disbelievers, the stubborn ungrateful, the deniers of truth,

2.) Explanation

From the etymogical meaning of the word 'kafara' is covering up, hiding the seeds in the earth (= satara), so the meaning is to hide the truth, further to deny it. Those who refuse to accept the heavenly message brought by a genuin prophet, although they know that it confirms the truth they had from earlier revelations.

The word kâfir also means those who actively deny the truth by attacking Islam or the Muslims by speech, pen or actions etc.

Another meaning of kâfir is of having a corrupt belief, as when distorting the original teaching of the Oneness of Allah.

It also means the one without God, an atheist and acting as such. On the Day of Judgement the kâfir is the one who died as a disbeliever. 2-161
(Ibn Kathir commenting on 2-254, says that there is no greater sin than meeting Allah as a disbeliever. )

He will be in Hell, because he did not have the least amount of faith in the One God.
It does not mean common people going their business, because if they respect Islam and the Muslims, they have to be respected as much, according to the teachings of the Quran and the Sunna. OT

3.) Some quranic definitions

3.1) The disbelievers are those who:

a.) disbelieve in Allah and His messengers,
and also believing in some, while rejecting others 4-150b.) and in the message which has been sent from God. 41-14e.) and they judge by someting else than what was revealed from above. 5-44
Ibn Abbas (ra) is reported to have said:
"(Oh Muslims!) Good people you are! The pleasant is for you, the unpleasant is for the people of the book. Whoever denies the decree of Allah is an unbeliever. Whoever accepts it, but does not judge according to it, is a wrongdoer (Zâlim)." Zamahs.c.) the believers have to be protected against. 109-1d.) because if they but knew - whiles wronging others, they wrong themselves (their souls). 2-254

3.2) Allah is the source of all grace and goodness

Allah is the source of all grace and goodness, so man owes God being grateful of all bestowed bounties. But the kâfir is not, and worse he even rebells against His Benefactor.

Here are some quranic verses of his reactions to truth and his character:

a.) they do not understand, do not try even, but wondering 50-2b.) they are astonished at the message 50-3, 38-4c.) they are ungrateful (original meaning of kfr) 26-19d.) they are mocking the message 21-36e.) they deny the message (core meaning of kfr) 29-47 g.) they have defective hearts 22-46f.) their pride is a consequence of their hardened hearts 7-75h.) the kâfir's mind described (hearts of stone) 2-74i.) their hearts are veiled, as if a curtain between it and Revelation 41-5.j.) a kind of (spiritual ignorance and sin) rust covers their hearts ever more 83-14k.) that is why they are in a state of deepest (self-)deception 67-20l.) but at times of distress the unbelievers' nature of kufr is made manifest 42-48m.) disputing, relying on reason only, not ready for meeting their Lord 32-10n.) the believers and prophets (as) do not despair, but so do the unbelievers 12-87

3.3) Verses on how the unbelievers are acting and reacting:

a.) As above mentioned they always act in pride and deny the message 6-29b.) they disbelieve in the Resurrection taking to reason instead of the Revelation 6-29 and 32-10 c.) they disbelieve in the signs (i.e. favours) / verses of Allah and deny them 3-70d.) they doubt anything which is not what they call "reasonable", f ex that a normal man was given prophethood. 54-24e.) there are against the truth of the Oneness of Allah (tauhîd) 38-5f.) they would deny the mentionng of the All-Beneficient (ar-RaHmân) 21-36 see aboveg.) there are arrogant 21-4h.) their contentiousness and their asking the Prophet embarrassing questions 40-4i.) what is worse the debar other people from the right path 11-19

3.4) Some quranic verses on the unbelievers unhaply ending:

a.) they will not be not successful, nor happy, not in bliss 28-82b.) Judgement-day will be a bad day for the unbelievers, a stern punishment 42-26c.) because they were used to call the divine truth being unreal or 'magic' 43-30d.) they will regret not having used their intellect 67-10

4.) Quranic advice

a.) Do not take them for friends, as long as they prefer disbelief for belief 9-23b.) It is a waste of time to try to guide them 27-80

5.) The quranic verses

4-150. Surely those who disbelieve in Allah and His apostles and
(those who) desire to make a distinction between Allah and His
apostles and say: We believe in some and disbelieve in others, and
desire to take a course between (this and) that.

4-151. These it is that are truly unbelievers, and We have prepared
for the unbelievers a disgraceful chastisement.

41-14. ... [the disbelievers] said: If our Lord had pleased He would certainly have sent
down angels, so we are surely unbelievers in that with which
you are sent.

109-1. Say: O unbelievers!
I do not serve that which you worship,
Nor do you serve Him Whom I worship...

2-254. ... and it is those who disbelieve that do wrong to
themselves.

5-44. ... and whoever did not
judge by what Allah revealed, those are they that are the unbelievers.

50-2. Nay! they wonder that there has come to them a warner
from among themselves, so the unbelievers say: This is a
wonderful thing...

50-3. What! when we are dead and have become dust? That is afar
(from probable) return.

38-4. And they wonder that there has come to them a warner from
among themselves, and the disbelievers say: This IS an
enchanter, a liar.

38-5. What! makes he the gods a single God? A strange thing is
this, to be sure!

26-19. And you did (that) deed of yours which you did, and you are one of the ungrateful.

21-36. And when those who disbelieve see you, they do not take you but for one to be scoffed at: Is this he who speaks of your gods? And they are deniers at the mention of the Beneficent God.

29-47. And thus have We revealed the Book to you. So those whom We have given the Book believe in it, and of these there are those who believe in it, and none deny Our communications except the unbelievers.

7-75. The chief of those who behaved proudly among his people
said to those who were considered weak, to those who believed
from among them: Do you know that Salih is sent by his Lord?
They said: Surely we are believers in what he has been sent with.
Those who were haughty said: Surely we are deniers of
what you believe in.

22-46. Have they not travelled in the land so that they should have hearts with which to understand, or ears with which to hear? For surely it is not the eyes that are blind, but blind are the hearts which are in the breasts.

2-74. Then your hearts became hardened after that, till they were like
stones or harder still; for of stones there are some out of which gush forth
streams, and of them there are some out of which flows water when they
cleave asunder. And indeed of them are some that humble themselves for the
fear of ALLAH. And ALLAH is not unmindful of what you do.

41-5. And they say: Our hearts are under coverings from that to
which you call us, and there is a heaviness in our ears, and
a veil hangs between us and you, so work, we too are
working.

83-14. Nay! rather, what they used to do has become like rust upon their hearts.

67-20. Or who is it that will be a host for you to assist you
besides the Beneficent God? The unbelievers are only in
deception.

42-48. ... if an evil afflicts them on account of what
their hands have already done, then - surely man is
ungrateful.

32-10. And they say: What! when we have become lost in the
earth, shall we then certainly be in a new creation? Nay!
they are disbelievers in the meeting of their Lord.

6-29. And they say: There is nothing but our life of this world,
and we shall not be raised.

6-30. And could you see when they are made to stand before
their Lord. He will say: Is not this the truth? They will say: Yea!
by our Lord. He will say: Taste then the chastisement because
you disbelieved.

3-70. O People of the Book ! Why do you deny the signs of ALLAH, while you
are witnesses thereof ?

54-24. So they said: What! a single mortal from among us! Shall
we follow him? Most surely we shall in that case be in sure
error and distress
Has the reminder been made to light upon him from among us? Nay! he is an insolent liar!
Tomorrow shall they know who is the liar, the insolent one.

38-5. What! makes he the gods a single God? A strange thing is
this, to be sure!

21-41. And certainly apostles before you were mocked at, then there befell those of them who mocked that at which they had mocked.

40-4. None dispute concerning the communications of Allah but
those who disbelieve, therefore let not their going to and
fro in the cities deceive you.

11-19. Who turn away from the path of Allah and desire to make
it crooked; and they are disbelievers in the hereafter.

28-82. And those who yearned for his place only the day before began to say: Ah! (know) that Allah amplifies and straitens the means of subsistence for whom He pleases of His servants; had not Allah been gracious to us, He would most surely have abased us; ah! (know) that the ungrateful are never successful.

42-26. And He answers those who believe and do good deeds, and
gives them more out of His grace; and (as for) the
unbelievers, they shall have a severe punishment.

43-30. And when there came to them the truth they said: This is
magic, and surely we are disbelievers in it.

67-10. And they shall say: Had we but listened or used our intellect,
we should not have been among the inmates of the burning fire.

9-23. O you who believe! do not take your fathers and your
brothers for guardians if they love unbelief more than belief; and
whoever of you takes them for a guardian, these it is that are the
unjust.

27-80. Surely you do not make the dead to hear, and you do not make the deaf to hear the call when they go back retreating.
27-81. Nor can you be a guide to the blind out of their error; you cannot make to bear (any one) except those who believe in Our communications, so they submit.

2-161. Those who disbelieve and die while they are disbelievers, on them
shall be the curse of ALLAH and of the angels and of men all together.